1. Field
This disclosure relates generally to compiling technologies in a computing system, and more specifically but not exclusively, to method and apparatus for merging critical sections when compiling a computer program.
2. Description
Multithreading and multiprocessing are common programming techniques often used to maximize the efficiency of computer programs by providing a tool to permit concurrency or multitasking. Threads are ways for a computer program to be divided into multiple and distinct sequences of programming instructions where each sequence is treated as a single task and to be processed simultaneously. An application that may use the multithreaded programming technique is a packet-switched network application that processes network packets in a high speed packet-switched system concurrently.
To maintain and organize the different packets, a new thread may be created for each incoming packet. In a single processor environment, the processor may divide its time between different threads. In a multiprocessor environment, different threads may be processed on different processors. For example, the Intel® IXA™ network processors (IXPs) have multiple microengines (MEs) processing network packets in parallel where each ME supports multiple threads.
In such a parallel programming paradigm, accesses to shared resources, including shared memory, global variables, shared pipes, and so on, are typically be protected by critical sections to ensure mutual exclusiveness and synchronizations between threads. Normally, critical sections are created by using a signal mechanism in a multiprocessor system. A signal may be used to permit the entering or to indicate the exiting of a critical section. For instance, in an Intel® IXP™, packets are distributed to a chain of threads in order (i.e., an earlier thread in the chain processes an earlier packet). Each thread waits for a signal from the previous thread before entering the critical section. After the signal is received, the thread executes the critical section code exclusively. Once this thread is done, it sends the signal to the next thread after leaving the critical section.
Due to hardware cost, the number of signals is limited by the scale of processing element. For example, each thread only has 16 signals in Intel® IXP™ MEs. Excessive use of critical sections may adversely impact the performance of a program. Therefore, it is desirable to efficiently use critical sections.